Systems are known which are capable of synthesizing 2-dimensional images in response to data defining elements within a 3-dimensional space. The final 2-dimensional result may consist of a very large number of coloured picture elements (pixels) which may be viewed on a monitor or printed onto an image carrying medium.
In interactive systems arranged to generate data representing a 3-dimensional space, objects appear to move within the 3-dimensional space in response to input commands. Thus, in such systems a machine is required to render a 2-dimensional image from data representing a 3-dimensional space and, in addition, the machine is also required to perform this operation repeatedly as the position and/or orientation of objects, light sources and the view point change in response to input commands. Typically, in an interactive environment, the machine is required to produce output images at a rate of between five to fifteen per second. In more highly powered environments, output images are produced at video rate (60 frames per second) and the machine is said to operate in real time.
In known machines, a detailed example of which will be described later, a significant amount of hardware is required if acceptable images are to be produced at an interactive rate. Thus, computational demands have placed significant constraints on 3-dimensional interactivity, thereby limiting the extent to which interactive 3-dimensional graphics may be employed.
Other examples of known systems are described in GB-A-2 246 497 and GB-A-2 207 585, both of Sun Microsystems, and EP-A-0 259 971 of AT&T. These and other documents in the prior art describe how the appearance of objects includes contributions from diffuse reflection and specular reflection. In the case of diffuse reflection, the relevant parameters are the orientation of the object surface and the direction and intensity of an illuminating light source. For specular reflection, it is known that the appearance of specular highlights is a very non-linear function of the orientation of the surface, the direction of illumination and also the direction of viewing.
Accordingly, it is well known that the representation of specularity in synthesised images is computationally very expensive. This is due partly to the need for non-linear calculations, typically requiring a number to be raised to a large power, but also to the fact that the view point generally varies continuously throughout an interactive or motion picture sequence, while the positional relationships between objects and light sources tend to remain constant.
It is an object of the present invention to provide apparatus and methods for processing image data, which require reduced computational overheads.
It is a further object of the present invention to provide apparatus and methods capable of producing acceptable images at an interactive rate but with lower computational demands.